1. Field of the Invention
This invention relates to improvements in a steering column for an automotive vehicle, and more particularly to the improvements in an energy absorbing configuration of the steering column to accomplish reduction in an initial load in a secondary collision of the automotive vehicle.
2. Description of the Prior Art
In general, in an automotive vehicle, a steering column is located below an instrument panel within a passenger compartment and secured inclined relative to a vehicle body. The steering column is provided with an energy absorbing configuration to absorb an impact energy when an impact load is applied to a steering wheel in a vehicle collision, in order to prevent a vehicle occupant from being injured upon the occupant's collision against a steering wheel. A variety of such energy absorbing configurations have been hitherto proposed and put into practical use. Such energy absorbing configurations basically include a first structure in which the steering column can axially contract, a second structure in which a bracket for supporting the steering column to a vehicle body can slide and get off from the vehicle body, and a third structure in which the bracket for supporting the steering column to the vehicle body can make its plastic deformation such as partial bending or breakage in a state to be fixed to the vehicle body. The first structure is arranged, for example, as follows: The steering column includes a steering shaft which consists of a rod-shaped lower shaft, and a pipe-shaped upper shaft. The lower shaft is axially fitted in the upper shaft, in which a molded resin is interposed between the lower and upper shafts to secure them. The steering column can axially contract when the molded resin is sheared upon receiving impact energy of the vehicle occupant. Recently, combination of the first, second and third structures has been increasingly used.
Now, a secondary collision occurs in the vehicle collision so that the vehicle occupant moves forward in parallel with a vehicle cruising direction and strikes against the steering wheel. It has been known that an impact load applied to the steering wheel produces a component force along the axis of the steering column and another component force perpendicular to the steering column axis.
In this connection, drawbacks have been encountered in the conventional steering columns provided with the energy absorbing configurations, as set forth below. That is, when the steering column moves forward with respect to the vehicle body upon receiving the impact load, an energy absorbing action by the above-mentioned second or third energy absorbing structure and another energy absorbing action by the above-mentioned first energy absorbing structure are simultaneously made. As a result, there is a tendency that an initial load becomes high in an impact energy absorption process during the secondary collision.